On 1/13/2019 1:49 PM, Alexis King wrote:
Disclaimer: this answer is extremely non-authoritative.
Ditto.
I think that, in Racket, the terms are used more or less
interchangeably. The technical term is “procedure”, but as you point
out, the term “function” is also used to mean the same thing. I don’t
believe there is any distinction there that would be universally
understood.
On the other hand, in How to Design Programs (and its various teaching
languages), my understanding is that “function” is the correct term
and “procedure” is strongly discouraged. The documentation on
implementing new teachpacks supports this understanding, in a section
entitled Prohibited Words
<http://docs.racket-lang.org/htdp/index.html#(part._.Prohibited_.Words)>.
It states explicitly that “function” should be used instead of
“procedure”, “selector”, “constructor”, or any number of other terms.
It includes the following justification:
These guidelines use few terms intentionally, emphasizing
commonality among concepts rather than technical precision (which
most students do not appreciate anyway).
I imagine others on this list who wrote the above words can give a
more authoritative answer should they find this one inadequate. :)
Alexis
Back in the day, "procedures" and "functions" were both considered a
form of "subroutine" [see compiler texts from 70s .. 90s]. They were
distinguished from inline (GOTO) subroutines by being lexically scoped
and taking arguments. Additionally, there was the distinction that
(like its mathematical counterpart) a "function" computed something and
returned a value (or values), while a "procedure" primarily was intended
to create side effects and (importantly) DID NOT return a value.
Pascal enshrined that last distinction in its syntax, but it existed
already in earlier languages.
Scheme uses the term "procedure" I *think* because it was influenced by
Algol. For whatever reason, Algol called subroutines "proc"
consistently regardless of whether they returned a value. Possibly
Algol's designers did that deliberately to avoid association with
mathematical "functions".
Racket began as PLT Scheme and remains (relatively) closely associated
with Scheme. So it's not surprising that there are wrinkles in the
documentation.
Aside: also back in the day, the term "pure procedural" referred to
programming without functions. PP subsumed the notion of CPS, but was
not synonymous with it - if the language supported it, procedures were
permitted [in Ada parlance] to have "OUT" or "INOUT" parameters, through
which results could be passed back up the call chain.
To Ellen: You might wish to educate your students re: the history. For
modern use I think Alexis is right - the terms are used more or less
interchangeably and the historical distinctions largely have become
meaningless.
YMMV,
George
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